Bistatic radars include a radar transmitter and a radar receiver that are remotely disposed to perform transmission and reception between remote positions.
It is known that bistatic radars use, as beams of the receiver, a wide-angle beam that covers all the area of a transmission beam or use a multi-reception beam in which a plurality of narrow-angled reception beams are formed with respect to all the areas in a transmission beam. Using the multi-reception beam can enhance a reception gain as compared with using the wide-angle beam, and can enhance a spatial resolution. However, the number of reception beams increases, and the scale of the device increases, which is problematic.
Thus, techniques for reducing the number of multi-reception beams have been proposed. For example, reduction criteria of the number of reception beams such as a signal detection rate and an angle measurement precision are provided, and the values such as a signal detection rate and an angle measurement precision are observed. Until the observed values satisfy the criteria, the beam widths continue to be widened. It is thereby possible to reduce the number of reception beams while satisfying a required minimum reception performance, resulting in reducing the scale of the device.
In bistatic radars used for detecting objects for aircrafts, vessels, or the like, such a method is effective in reducing the number of reception beams, but in the case of bistatic radars for meteorological observation (bistatic weather radars), there is a problem in which the observation cannot be performed with high precision by such a method.
Bistatic weather radars have received radio waves reflected by raindrops (scattering particle) which are in the volumes enclosed by a beam from a transmitter and beams from a receiver. Since an observed signal is a composition of scattered signals from the particles in the observed area, weather conditions are estimated by statistics of observed signal in weather radar. For this reason, if there is a large deviation in the observed volumes at which the transmission beam intersects the reception beams, the statistical properties are not even, in other words, variations in precision of The observation arise between the observed areas. In the above-described method that has been proposed, the deviation in the volumes of the observed areas readily arises, and thus the variations in precision of the observation arises, which makes observation with high precision difficult.